为探讨稀土元素镱对镁的合金化作用，制备了Yb含量分别为0.5、1、2、3、4和8%（质量分数）的Mg-Yb和Mg-Yb-0.5Zr系列镁合金．用光学显微镜、扫描电镜和电子探针等对合金的显微组织和相结构进行了观察和分析，并进行了拉伸实验和硬度测试．发现随着Yb含量的增加，Mg-Yb二元合金的晶粒明显细化，但少量的Yb（≤4％）并不能改变合金原来的晶粒形态；添加0.5% （质量分数）的Zr使Mg-Yb二元合金全部得到细小的等轴晶粒，合金的强度和硬度明显提高．当Yb含量达8 % 时，因强烈的成分过冷促使等轴枝晶的形成，晶界处的Mg2Yb由断续的条块状变为连续网状，并出现共晶组织，合金的强度和延伸率降低．实验证明，稀土元素镱对镁具有良好的细化晶粒和强化作用，Zr是Mg-Yb合金非常有效的晶粒细化剂．
To understand the alloying effects of a heavy rare earth metal, ytterbium, in magnesium, two series of Mg-Yb and Mg-Yb-0.5Zr magnesium alloys were prepared using flux protection with Yb additions of 0.5, 1, 2, 3, 4 and 8 % (mass fraction), respectively. Microstructure analyses and mechanical properties tests of the alloys were performed by use of optical microscope, X-ray diffraction, differential scanning calorimeter, Scanning electric microscope and electro-probe, et al. It is found that adding ytterbium in pure Mg can refine grain sizes remarkably but not change the primary columnar morphology below 4% Yb contents. All Mg-Yb binary alloys obtained fine equiaxed grains with the addition of 0.5% (mass fraction) zirconium. The tensile strengths and hardness of the alloys increase with the increase of Yb contents. In the case of high Yb content, 8%, the strength and elongation drops sharply due to the formation of continuous network Mg2Yb intermetallics and eutectic structures on grain boundaries. The results show that ytterbium has refining and alloying effects on magnesium and zirconium was an effective grain refiner in Mg-Yb binary alloys.
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